ABSTRACT Pulmonary hypertension (PH) is characterized by pulmonary vasculature remodeling and elevated pulmonary artery pressure that leads to progressive right-sided heart failure and death. Growing evidence indicates that genetic susceptibility, inflammation, and metabolic shifts in the pulmonary vasculature play key roles in PH pathogenesis. The mechanisms that underlie PH remain enigmatic because of its tremendous complexity. Consequently, current therapy for PH is limited primarily to vasodilation. In this application, we target one of the more proximal signaling hubs in the pathogenesis of PH?insulin receptor substrate 2 (IRS2), a critical molecule in insulin resistance and cellular energy homeostasis. Because IRS2 is the main regulator of insulin and insulin growth factor signaling, loss of IRS2 expression promotes insulin resistance and type II diabetes. Indeed, the loss of IRS2 appears to be deleterious in multiple cell types and disease conditions. Although the role of IRS2 in insulin signaling has been studied, very little is known about its contribution to cardiopulmonary pathophysiology, including that seen in PH. Our preliminary data show that IRS2 expression is decreased in hematopoietic cells of patients with pulmonary arterial hypertension and that IRS2 deletion exacerbates macrophage activation to pro-PH phenotype, and perivascular muscularization in a mouse model of PH. Based on our data and other published results, we hypothesize that IRS2 possesses anti-inflammatory and anti-hyper-proliferative activity in the pathogenesis of PH, and that loss of IRS2 in bone marrow-derived cells enhances vascular inflammation and promotes a hyper-proliferative microenvironment. Hence, IRS2 might be valuable as a novel biomarker for PH, and restoring IRS2 expression and function might represent a novel therapeutic target for multifactorial PH pathophysiology. Specific Aim 1 will investigate the correlation between IRS2 expression in lymphoid cells and the clinical characteristics of patients with pulmonary arterial hypertension. Specific Aim 2 will determine the anti-inflammatory role of macrophage-derived IRS2 in pulmonary vascular remodeling and PH development and examine whether IRS2 influences macrophage activation to a pro-PH phenotype. Specific Aim 3 will test the hypothesis that IRS2 and 5' adenosine monophosphate-activated protein kinase (AMPK) signaling integrate several key pathways implicated in pulmonary artery smooth muscle cell proliferation and that restoring IRS2 by adenoviral gene therapy will reverse experimental PH. The goal of this proposal is to unravel the unrecognized protective role of IRS2? specifically its ability to suppress inflammation and hyper-proliferative activity during PH development. Thus, the data generated will support the development of new agents that target multiple downstream inflammatory, neoplastic, and metabolic mediators of this pathway that can be used for treatment of right heart failure and PH.